Field of the Invention
This invention is directed to rotary foundation pile drilling technology and in particular to a drill tip for screw-type foundation piles that has an improved ability to penetrate the soil.
Discussion of the Prior Art
Deep foundations are widely used as foundation elements for structures. Two well known classes of piles are non-displacement piles and displacement piles. The former are installed by excavating a cylinder of soil from the ground and replacing it with some form of reinforcement, commonly, concrete. By far the most common method of excavating the soil is by use of an auger, giving rise to the term auger cast-in-place (ACIP) piles.
Displacement piles are either driven or drilled into the ground. Displacement piles laterally displace soil surrounding the pile shaft and load soil materials below the toe of the pile. Displacement piles are generally understood to have a stiffer response than non-displacement piles, and are capable of carrying larger loads than non-displacement piles. However, driving piles into the ground can result in excessive vibration and noise and are, therefore, problematic under certain conditions. Drilled displacement piles are rotary displacement piles installed by inserting a cylindrical soil displacement body into the ground with the combined application of torque and vertical force, the latter commonly referred to as “crowd.” The soil displacement body may include single or multiple helices that help penetrate and laterally displace the soil. An auger tip is attached to the bottom end of the cylindrical body. Drilled displacement piles have favorable end bearing and skin friction capacities compared to ACIP piles. However, to install drilled displacement piles expensive specialty equipment is required that produces tremendous torque and crowd forces to drive the pile into the soil. An installation process that is less efficient correspondingly increases the expense of the foundation. There is, therefore, a need for improved drilled displacement piles to reduce the power requirements and expense associated with their installation.